1. Field of the Invention
The present invention relates to an abnormality determining method for determining the presence of an abnormality in a detection subject on the basis of a result obtained by information obtaining means for obtaining information about an object, and also to an abnormality determining apparatus and image forming apparatus using this method.
2. Description of the Background Art
In a conventional image forming apparatus such as a copier, facsimile, or printer, maintenance is required to replace consumables (toner, for example) and components (a photosensitive body, for example), repair faults, and so on. When a fault occurs, the device must be halted from the occurrence of the fault to the completion of repairs, causing a great time loss for the user. It is therefore desirable to predict the occurrence of a fault in the image forming apparatus, the end of the life of a component, and so on in order to provide the user with a maintenance preparation period, thereby reducing the amount of downtime. It is also desirable that downtime be reduced in various devices, such as manufacturing machines and electric appliances, as well as image forming apparatuses.
In a proposed image forming apparatus which is capable of making such a prediction, predetermined information regarding the interior of the device is obtained by information obtaining means such as a sensor, and early detection of an abnormality in the device is performed by comparing the obtained information with prestored normal index information. In Japanese Unexamined Patent Application Publication H5-281809 (Prior Art 1), for example, an image forming apparatus is proposed in which driving load information regarding a driving source, serving as predetermined information, is detected, and early detection of an abnormality in the driving system is performed by comparing the detection result with a standard value serving as normal index information. According to this constitution, by detecting an abnormality in the driving system before a fault occurs, a user can be provided with a maintenance preparation period for preparing replacement components or the like.
In this image forming apparatus, however, abnormalities are not always detected at a timing which is appropriate for the user. This is due to the following reason. For example, a user who is highly conversant with the image forming apparatus may be able to repair a fault in the image forming apparatus that a general user could not repair. In such a case, the user would not contact a repair service organization to request repairs. If a serviceperson is dispatched nevertheless on the basis of the predicted fault, the resulting wasted labor would lead to an increase in service costs. Moreover, depending on the type of fault, each user has a widely differing perception thereof. For example, one user may suspect a fault in the paper feeding system even when a paper jam occurs rarely, whereas another user may not suspect a fault in the paper feeding system even when paper jams occur comparatively frequently. In the case of the latter user, repair requests are rarely made, even if a serviceperson is dispatched at the stage when the abnormality in the paper feeding system has barely begun to occur. This manner of dispatch also leads to an increase in service costs.
Meanwhile, a remote fault diagnosing system described in Japanese Unexamined Patent Application Publication H8-30152 (Prior Art 2) is known as a system in which abnormalities can be detected at a timing that is appropriate for the user. In this remote fault diagnosing system, basic diagnosis data transmitted from a plurality of image forming apparatuses serving as diagnosis subjects are received in a central diagnosing device, and various abnormalities in the individual image forming apparatuses are diagnosed on the basis of these basic data. These various abnormalities include a paper feeding abnormality, an image quality abnormality, and so on. By diagnosing the various abnormalities respectively, a fault in the paper feeding system or image forming system caused by the progression of the diagnosed abnormality can be predicted before its occurrence. Moreover, when diagnosing the various abnormalities, the remote fault diagnosing system takes into account the proficiency of the user of the image forming apparatus and the degree of perception of the fault. In so doing, abnormality diagnosis can be performed in accordance with the individual user, thus enabling a reduction in service costs. Note that as a result of dedicated research, the present inventors have discovered that, from among various abnormalities, the degree of perception of each user varies particularly widely in regard to an abnormality in the image quality.
A Mahalanobis Taguchi System, described in the Japanese Standards Association publication “Technical Developments in the MT System” by Genichi TAGUCHI (Prior Art 3), is known as a method of measuring the degree of normality in the state of an object. This MTS method measures the degree of normality in the state of an object in the following manner. First, a plurality of normal values relating to a group of information comprising a plurality of types of information indicating the state of a detection subject is obtained, and a normal group data set is constructed therefrom. To take a medical examination as an example, first normal values comprising the gender, various blood test results, height, weight, and so on of a healthy person are obtained in advance from a plurality of healthy people, and a normal group data set is constructed therefrom. Next, a multidimensional space is constructed on the basis of the normal group data set. The Mahalanobis distance, which indicates the position of the grouped information obtained from the detection subject in this multidimensional space, is then determined, and an evaluation is performed to determine the degree of similarity between the grouped information for the detection subject and the normal group data set. According to this MTS method, the degree of normality of the detection subject can be determined comprehensively on the basis of the correlation among the various information.
The present inventors learned through experience that in a conventional image forming apparatus, faults include those having a clearly identified cause, such as an abnormality in the driving system or the like, and those which do not have a clearly identified cause. In the latter case, even when an obvious abnormality cannot be identified in the individual members of the mechanical location (process cartridge or the like) that is believed to be the cause of the fault, the fault (an abnormal image or the like) disappears when the entire mechanical location is replaced.
In the image forming apparatus of the aforementioned Prior Art 1, in which an abnormality in the device is detected early by comparing the obtained results of predetermined information such as driving load information and the like with normal index information, a fault can be predicted in advance through early detection of the abnormality. However, since the fault occurs due to the progression of the detected abnormality, faults without a clearly identified cause cannot be predicted.
Hence the present inventors are currently developing a novel abnormality determining apparatus which is capable of predicting the occurrence of a fault without a clearly identified cause using the MTS method (this abnormality determining apparatus will be referred to as the “device in development” hereafter). The device in development stores data relating to a multidimensional space constructed on the basis of a normal combined data set comprising a photosensitive body charging amount, temperature, feed speed, and so on of an image forming apparatus serving as the detection subject. The Mahalanobis distance in the multidimensional space is then determined for the combined data (detected data) obtained during an image forming operation, and a determination is made as to whether or not an abnormality is present. With this constitution, unlike the image forming apparatus of Prior Art 1, the occurrence of a fault without a clearly identified cause can be predicted by determining the presence of an abnormality in combined data detected by a sensor or the like.
However, the present inventors discovered that, in this device in development, a normal state is sometimes detected mistakenly when an abnormality is present. More specifically, in a typical image forming apparatus, for example, a user may often select between a high speed mode, in which high speed printing takes priority over high image quality, and a high image quality mode, in which high image quality takes precedence. With this type of constitution, in which the user may select from a plurality of operating modes, the normal value of the paper conveyance speed in the device differs according to the operating mode setting. More specifically, the normal value of the paper conveyance speed is approximately 100 [mm/sec] in the high speed mode, but approximately 50 [mm/sec] in the high image quality mode. Hence if a multidimensional space is constructed on the basis of a normal data set obtained while mixing the plurality of modes, a detection data value of 75 [mm/sec] for the paper conveyance speed is mistakenly detected as normal when it should be detected as abnormal. In a typical image forming apparatus, detected data regarding the toner bulk density, electric resistance value, and so on may also have different normal values according to the environment (temperature and humidity). However, if a multidimensional space is constructed on the basis of a normal data set detected in a plurality of environments, a similar misdetection occurs.
The reason for these misdetections is that, despite the fact that the normal values of information results obtained by the information obtaining means differ according to the content of specific information such as the operating mode setting and environment, the determination as to the abnormality of the information is performed on the basis of only one normal data set. Note that the occurrence of such misdetections is not limited to a case in which an abnormality is determined using the MTS method, and may occur with any abnormality determining method that uses only one set of normal index information such as a normal data set.
Meanwhile, in the remote fault diagnosing system of the aforementioned Prior Art 2, although faults are diagnosed in consideration of the user's proficiency and perception of the fault, when the user changes, it is impossible to take into account an appropriate degree of proficiency and fault perception for the new user. As a result, faults cannot be notified at an appropriate timing for the new user.
Moreover, the fault diagnosing system of Prior Art 2 diagnoses a plurality of abnormalities occurring inside the diagnosis subject image forming apparatus individually. Therefore, as the types of abnormality to be diagnosed increase, the calculation amount required for the diagnoses rises, making control more complicated.
With the device in development described above, such increasingly complicated control can be suppressed. The reason for this is as follows. In the device in development, various abnormalities in a detection subject such as an image forming apparatus are determined comprehensively as a single general abnormality, rather than individually. When at least one of the various abnormalities occurs, a general abnormality determination of “abnormality present” is made comprehensively. In so doing, increasingly complicated control due to an increase in the types of abnormality in the determination subject can be suppressed, unlike the remote fault diagnosing system of Prior Art 2, in which control becomes more complicated as the types of abnormality used in the determination increase.
However, the device in development is unable to determine various abnormalities in consideration of the user's proficiency and degree of fault perception. As a result, the abnormality determination precision is not always suited to the user, and depending on the user, abnormalities may be detected unnecessarily, the detection timing may be too late, and so on.
Further, when a general abnormality is determined as “present”, as in the device in development, using a method of perceiving the degree of deviation from a normal state, rather than perceiving the presence of individual abnormalities, the maintenance response following the detection of an abnormality becomes complicated. This is because it is difficult to specify the type of abnormality that has occurred from among all of the abnormalities that may be incorporated in the general abnormality.